Determination of normative neck muscle morphometry using upright MRI with comparison to supine data

Neck muscles are important in the static and dynamic stability of the head-neck complex. Deep neck muscles act to maintain upright posture and superficial muscles are responsible for gross movements. Previous studies have quantified neck muscle geometry using traditional supine magnetic resonance imaging (MRI). However, supine orientation removes the vertical load on the cervical spine from the head-neck complex and changes the relative orientation of the spine and neck muscles. Therefore, the purpose of this study was to demonstrate the feasibility of upright MRI to obtain neck muscle morphometric data on a spinal level-by-level basis for subjects in upright seated positions.

Upright MRI scans were obtained of the neck region for six younger male volunteers in neutral and flexed positions. Planar images were oriented parallel to the intervertebral disc space at each level. Cross-sectional area (CSA) and orientation of neck muscles were quantified at four spinal levels.

Area and position of all four muscles were significantly dependent upon spinal level. Average CSA of the sternocleidomastoid, longus colli, levator scapulae, and trapezius muscles in neutral position were 512, 113, 281, and 174 mm2. Head-neck position significantly affected area and position of the sternocleidomastoid and position of posterior neck muscles.

Comparison of neck muscle areas from the present study to a previous study incorporating supine MRI demonstrated differing trends between anterior and posterior neck muscles that may be attributable to upright orientation of volunteers and planar image orientation in the present study. Differences between supine and upright MRI identified in the present study may warrant incorporation of this technique in future spinal imaging studies.